With the means presently available, mainly surgery and radiation, cancer can be cured if the diagnosis is made early, before the cancer has spread too far to permit removal by the surgeon or destruction by radiation. The clinical manifestations are frequently late in the natural history of cancer. The early clinical findings require, as a rule, a biopsy for a diagnosis. The pathologist can (1) exclude cancer; (2) find changes, leaving no doubt as to the malignant nature, the cancer may at that time be already invasive; (3) anaplasia may be moderate; or (4) cells with morphologic criteria of cancer may be present close to normal cells (carcinoma-in-situ). It is in the latter group that pathologists may disagree. It was established by follow-up of patients with carcinoma-in-situ of the cervix that some lesions of this type may be reversible. Treating such patients as having carcinoma may lead to unnecessary surgery. On the other hand, failure to be radical may deprive such patients of the benefits of surgery. Clinical manifestations of metastases may be late. Examination of the primary lesion does not enable the pathologist to diagnose metastases. The highly sensitive and specific Red Cell Adherence (RCA) test detects the A, B and H antigens in tissues and permits one: (1) to diagnoses some carcinomas earlier than does any other method now available and (2) to demonstrate the possibility or even probability of metastases, or to make their presence less likely. The quantitative test which we developed increases the sensitivity of the adherence test. We will continue to test our results by studying prospectively and retrospectively a larger number of early and advanced cancers in different organs.